brown, which your perceptive mechanism classes with the appearance of a cow at such a distance; and instantly all the other properties of a cow are supplied from the resources of former experience:  but on getting nearer, it turns out to be a log of wood.  It is some protection against such errors to know that we are subject to them; and the Logician fulfils his duty in warning us accordingly.  But the matter belongs essentially to Psychology; and whoever wishes to pursue it will find a thorough explanation in Prof.  Sully’s volume on Illusions.

Another error is the accumulation of useless, irrelevant observations, from which no proof of the point at issue can be derived.  It has been said that an important part of an inductive inquirer’s equipment consists in knowing what to observe.  The study of any science educates this faculty by showing us what observations have been effective in similar cases; but something depends upon genius.  Observation is generally guided by hypotheses:  he makes the right observations who can frame the right hypotheses; whilst another overlooks things, or sees them all awry, because he is confused and perverted by wishes, prejudices or other false preconceptions; and still another gropes about blindly, noting this and docketing that to no purpose, because he has no hypothesis, or one so vague and ill-conceived that it sheds no light upon his path.

Sec. 6.  The second kind of extra-logical Fallacy lying in the premises, consists in offering as evidence some assertion entirely baseless or nugatory, but expressed in such a way as to seem like a general truth capable of subsuming the proposition in dispute:  it is generally known as petitio principii, or begging the question.  The question may be begged in three ways: 

(1) There are what Mill calls Fallacies a priori, mere assertions, pretending to be self-evident, and often sincerely accepted as such by the author and some infatuated disciples, but in which the cool spectator sees either no sense at all, or palpable falsity.  These sham axioms are numerous; and probably every one is familiar with the following examples:  That circular motion is the most perfect; That every body strives toward its natural place; That like cures like; That every bane has its antidote; That what is true of our conceptions is true of Nature; That pleasure is nothing but relief from pain; That the good, the beautiful and the true are the same thing; That, in trade, whatever is somewhere gained is somewhere lost; That only in agriculture does nature assist man; That a man may do what he will with his own; That some men are naturally born to rule and others to obey.  Some of these doctrines are specious enough; whilst, as to others, how they could ever have been entertained arouses a wonder that can only be allayed by a lengthy historical and psychological disquisition.